linux-kgdb-qemu.md

• Create root file system image

cd $IMAGE/
wget https://raw.githubusercontent.com/google/syzkaller/master/tools/create-image.sh -O create-image.sh
chmod +x create-image.sh
./create-image.sh

-d buster for Debian 10, and -s 16384 for larger disk size.

• Kernel configuration

CONFIG_CONFIGFS_FS=y
CONFIG_SECURITYFS=y
CONFIG_KGDB=y
CONFIG_DEBUG_INFO=y

• Failed to start Raise network interfaces?

root@syzkaller:~# cat /etc/network/interfaces
# interfaces(5) file used by ifup(8) and ifdown(8)
# Include files from /etc/network/interfaces.d:
source-directory /etc/network/interfaces.d

auto eth0
iface eth0 inet dhcp

If the interface name from network/interfaces is dirfferent from the output of ip a, then add the following udev rule.

root@syzkaller:~# cat /etc/udev/rules.d/10-rename-network.rules
SUBSYSTEM=="net", ACTION=="add", ATTR{address}="52:54:00:12:34:56", NAME="eth0"

• QEMU

qemu-system-x86_64 \
        -m 4G \                                
        -smp 8 \
        -kernel `pwd`/arch/x86/boot/bzImage \
        -append "root=/dev/sda earlyprintk=serial rdinit=/bin/sh kgdboc=ttyS0,115200 kgdbwait rodata=off nokaslr" \
        -drive file=`pwd`/../stretch.img,format=raw \                                                              
        -net user,host=10.0.2.10,hostfwd=tcp:127.0.0.1:10021-:22 \
        -net nic,model=e1000 \                                    
        -enable-kvm -serial tcp::1234,server,nowait

If rodata=off nokaslr is not given, then you will not be able to set breakpoints with gdb.

• Set gdb target

(gdb) target remote localhost:1234

• Trigger breakpoint

# echo g > /proc/sysrq-trigger

Then it invokes kgdb_breakpoint.